The invention relates to a device and a method for the automatic inspection of ophthalmic lenses, especially contact lenses, in an automatic lens manufacturing process.
The production of contact lenses using conventional methods, such as rotary processes for hard contact lenses and pouring processes for soft contact lenses in disposable plastic moulds is relatively expensive. As a rule, these contact lenses are used in a period of one year to one month. Technical advancement in recent years, however, has enabled contact lenses to be produced, which are worn only on one day and are replaced afterwards by new contact lenses. However, this has been made possible only through a high degree of automation of the production plants. Production of these contact lenses advantageously takes place using reusable mould halves, the matrix and the patrix, which normally consist of glass or quartz. Between these mould halves is a hollow cavity, which corresponds to the subsequent contact lens shape. Before closing the mould halves, a polymer solution is measured into the matrix. UV light is radiated over the upper mould half, which leads to crosslinking of the lens material. Subsequently, the lens is removed from the mould half with suction grips and is placed in the pack.
In order to assure constant quality of the contact lenses, provisions are in place for automatic inspection of the contact lenses using industrial image processing methods. In image processing, the lenses are tested both in the mould halves and at the vacuum grips. An image processing method of this kind is described for example in EP patent 491663. Of course, not all defective contact lenses can be detected by this type of inspection, or nominal defects are established, such as bubbles formed by water spillages, which however illustrate artefacts. By having to sort out the perfect lenses, the yield is reduced, which has a negative effect on balancing the costs.
The invention is based on the problem of providing an inspection device and an inspection method, which recognises the defective lenses with a high degree of reliability, but does not falsely sort out perfect lenses. In particular, the image-processing system should carry out a complete examination of the contact lenses for accuracy of size, surface defects, tears, peripheral ruptures and inclusions such as bubbles and foreign bodies.
The invention solves this problem with the features of claim 1 and claim 21. As far as further essential developments of the equipment according to the invention and of the process are concerned, reference is made to the dependent claims.
Through the combination of the schlieren method and the transmitted light process, the advantages of both systems can be linked, so that defects can be evaluated more objectively. The schlieren method is in a position to illustrate the edge and its ruptures in high contrast for the CCD camera. Likewise, tears and surface defects can be made visible. With the transmitted light process, the bubbles can be appropriately prepared for the camera, so that defects can all be recognised in terms of the required test criteria.